1. Field of Invention
The invention generally relates to optical communication receivers. The invention more particularly relates to optically pre-amplified receiver nodes.
2. Description of Related Art
In conventional long-haul optical communications applications, the loss between the laser transmitter and the receiver is typically fixed or otherwise substantially invariant. Therefore, a gain block with fixed optical gain serves the purpose of ensuring that the receiver will receive a signal within the receiver""s dynamic range.
In some applications such as metropolitan optical ring networks, however, the loss between the laser transmitter and the receiver often changes due to changes in the span loss or due to channel upgrades. During channel upgrades, extra OADMs (optical add drop multiplexers) are added into the optical path of existing channels, therefore the loss between the transmitter and the receiver changes.
Furthermore, a complete fiber cut, fiber disconnect or other major fault in either a long haul or metro application can cause a loss of signal. As recognized by the inventors, the restoration of the optical signal following a loss of signal event may damage the receiver and/or cause bit errors.
Hence, in these applications a smart pre-amplified receiver is needed that will adapt to changing conditions such as those outlined above.
The invention includes an apparatus for optically preamplifying a signal being input to a receiving device, comprising: an optical amplifier optically coupled to an input port of the receiving device, said optical amplifier optically amplifying an input signal and outputting the optically amplified signal to the receiving device; a pump optically coupled to said optical amplifier, said pump injecting pumping light into said optical amplifier to provide the optical amplification of the input signal; and a controller operatively connected to said pump and to the receiving device, said controller receiving power measurements from the receiving device indicative of the amplified signal""s optical power; said controller commanding a pump power level output by said pump to perform gain control according to the power measurements received from the receiving device; and said controller setting the commanded pump power level of said pump to a home gain value upon an occurrence of a loss of signal event.
The controller may declare the loss of signal event when the power measurement received from the receiving device drops below a loss of signal threshold value.
Alternatively, the controller may declare the loss of signal event when the commanded pump power level is equal to or greater than a pump power level threshold value.
In another alternative, the controller may receive pump output power measurements from said pump indicative of said pump""s output power; and said controller may declare the loss of signal event when the pump output power measurement is equal to or greater than a pump output power level threshold value.
In yet another alternative, the controller may receive a declaration of the loss of signal event from an input port of said controller. A service channel may transmit the loss of signal declaration to the input port of said controller.
An optical bandpass filter may also be included to optically communicate with an output of said optical amplifier and an input of the receiving device, said optical bandpass filter having a bandpass including a center wavelength of the input signal.
The controller may also reinstate the gain control according to the power measurements received from the receiving device when the loss of signal event has ended.
Furthermore, when the loss of signal event has ended said controller may command the pump power level of said pump to a last pump power level commanded before the occurrence of a loss of signal event.
The invention further includes a method of optically preamplifying a signal being input to a receiving device with an optical amplifier optically communicating with an input of the receiving device, comprising: receiving power measurements indicative of the amplified signal""s optical power; commanding a pump power level of a pump optically coupled to the optical amplifier, the pump injecting pumping light into the optical amplifier to provide the optical amplification of the input signal; controlling said commanding step to perform gain control according to the power measurements received by said receiving step; and setting the commanded pump power level of the pump to a home gain value upon an occurrence of a loss of signal event.
The method may declare the loss of signal event when the power measurement received by said receiving step drops below a loss of signal threshold value.
Alternatively, the method may declare the loss of signal event when the commanded power level commanded by said commanding step is equal to or greater than a pump power level threshold value.
In another alternative, the method may receive pump output power measurements from the pump indicative of said pump""s output power; and declare the loss of signal event when the pump output power measurement is equal to or greater than a pump output power level threshold value.
In yet another alternative, the method may receive a declaration of the loss of signal event.
The method may also reinstate gain control according to the power measurements received by said receiving step when the loss of signal event has ended.
In addition, the method may command the pump power level of the pump to a last pump power level commanded before the occurrence of a loss of signal event.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.